Method of aligning the end faces and the acoustic axis of quartz delay lines for improving their acoustic response



May 12, 1970 J, D, Y U 3,511,987 METHOD OF ALIGNING THE END FACES AND THE ACOUSTIC AXIS OF QUARTZ DELAY LINES FOR IMPROVING THEIR ACOUSTIC RESPONSE Filed. May 23, 1967 INVENTORE do/m 0 yen/1Y4 United States Patent Ofiice U.S. Cl. 25042 3 Claims ABSTRACT OF THE DISCLOSURE By subjecting quartz rod delay lines to an X-ray field the acoustic axis within the quartz is made more nearly perpendicular to the end faces of the quartz crystal, and through a bending of the rod by the X-rays the end faces are made more nearly parallel to each other.

BACKGROUND OF THE INVENTION This invention is in the field of electro-mechanical delay lines and more particularly in the field of high frequency (100 mHz. to 50 gHz.) single crystal quartz delay lines.

Single crystal quartz rod delay lines are well known in the art, having been used in radar and allied electronic systems for several years. A difliculty has always been the fabrication of quartz rod delay lines that will provide a predicted total time delay, have a minimum of distortion or modulation of the pulse envelope, and that will not occasionally have a missing pulse at the output.

At gHz. the acoustic wavelength is 5000 A. and the required dimensional tolerances for efficient acoustic propagation through the crystal are approximately 500 A. Thus for good acoustic response the end faces of the crystal should be perpendicular to the acoustic propagation axis to less than seconds of arc. These tolerances are more stringent than the present grinding and lapping techniques provide. The disclosed radiation technique provides a method whereby a crystal can be corrected for the misalignment of the acoustic axis With the end faces of the crystal.

SUMMARY This invention provides a method of improving the acoustic propagation characteristics in crystal delay lines by bending the crystal so that the end faces of the crystal are made more nearly parallel.

This invention provides a method of internally rotating the propagation vector within a crystal delay line so that it is more nearly perpendicular to the end faces.

This invention provides a method of determining the optimum X-ray radiation of crystal delay lines for best acoustic progagation characteristics.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates the radiation by X-rays of a crystal cylindrical rod delay line.

FIG. 2 is an end view representation of FIG. 1.

FIG. 3 illustrates in an exaggerated manner the effect on the end faces of a crystal rod brought about by the radiation of the rod with X-rays; FIG. 3a being before radiation and FIG. 3b being during radiation.

DESCRIPTION OF THE PREFERRED METHODS Referring to FIG. 1, a conventional single crystal quartz cylindrical rod delay line 1 having essentially parallel end faces 2 and 3 is radiated with X-ray energy 4. The acoustic propagation, providing the delay, is axially through the rod between the faces. Thus the X-rays 3,511,987 Patented May 12, 1970 4 are directed on the quartz crystal at right angles to the direction of the acoustic propagation in the quartz. X- rays from a tungsten source (50 kv. at 50 ma.) have been found to provide a suitable source of radiation. Other radiant energy fields may be used such as neutron radiation, and electron radiation. It has been found to be desirable to expose an appreciable portion of the cylindrical length (approximately 50 to percent) of the quartz rod to the X-rays but not the end faces. The side of the crystal closest to the X-ray source receives the greatest amount of radiation as the radiation penetrates the crystal. FIG. 2 is an end view representation of the view of FIG. 1. While the thickness of the radiation 5 is shown to be approximately equal to the diameter of the crystal rod 1, the thickness of the radiation beam 5 is not critical provided it is at least approximately the diameter of the rod.

FIG. 3a shows a distorted exaggerated picture of a crystal rod 30 having nonparallel end faces 31 and 32. FIG. 3b portrays the same rod during radiation. The X-rays 33 have penetrated the side of the rod next to the source and the resulting strain gradient has caused the crystal to bend, making the end faces 31 and 32 more nearly parallel. The crystal retains the physical configuration it assumed during radiation after the radiation field is removed. It may be further radiated, additionally, after removal from the first radiation field, or, by annealing the quartz crystal rod at approximately 500 C. all the effects obtained by the radiation may be removed and the crystal will return to its pre-radiation acoustic response characteristics.

It is apparent that the direction of the radiation on the rod and the amount of radiation are critical. In FIGS. 3a and 3b it is seen that had the radiation 33 struck the rod 30 from the bottom side instead of the top side (as pictured) the faces 31 and 32 would have departed more than ever from being parallel. Likewise, had too much bending occurred from too much radiation, the end faces would have passed through an optimum parallel condition and proceeded on to another nonparallel condition sloped in the other directions from that pictured in FIG. 3a.

The best acoustic response (i.e., greatest total time delay to the signal propagating through the crystal, the least distortion of the signal, and the least number of missing pulses) is obtained when the end faces of the crystals are parallel and perpendicular to the axis of propagation of the signal through the crystal. Thus the propagation time is used to determine the amount and direction of the radiation to which the crystal is exposed. After proper alignment of the end faces and the acoustic axis not only is the acoustic response of the crystal improved from a total time delay standpoint, but unwanted modulation of the signal by the delay line is lessened and missing pulses are essentially eliminated.

In one embodiment of this method a BC cut (shear wave) quartz rod was given'successive increasing step amounts of 15-minute doses of X-ray radiation, and after each dose the propagation time, using a 10 gHz. signal at 42 K., was measured. (The radial direction of the impinging radiation had been previously determined as will be set forth later.) The peak power in the cavity was 10 watts. The initial delay response of the crystal was 350 microseconds. After 15 minutes of radiation the delay time was 925 ,usec.; after 30 minutes, 1.1 msec.; after 60 minutes, 1.2 msec.; after minutes, 1.4 msec.; after minutes, 1.6 msec.; after minutes, 1.4 msec., and after minutes it was 820 sec. Thus, in a plot of delay time vs. radiation time, the time delay was sharp on both the rise (0 to 15 minutes of radiation) and the tall (135 to 150 minutes) with an approximately level constant maximum therebetween. Missing pulses that frequently occurred in the unradiated crystal all filled in after approximately 90 minutes of radiation. In the region from 90 to 120 minutes of exposure to radiation, the acoustic response underwent only minor changes. The peak acoustic response after 120 minutes of X-ray radiation was 4.57 times the initial response. In this instance any time between 60 and 120 minutes of radiation is generally considered to be a suitable amount of radiation, at the power level used, to greatly improve the characteristics of the delay line.

To determine the orientation of the radiation field (that is, the radial direction from which the radiant energy impinges on the rod) it has been found desirable to divide the end face of the crystal rod into quadrants (labeled 0, 90, 180 and 270 degrees). Any arbitary reference is suitable. A relatively small, determined, equal, amount of radiation is then directed at each quadrant and the delay time measured. The crystal is annealed after each quadrant measurement before proceeding to radiating the next quadrant. Assume that radiation from an azimuth angle of 270 degrees in direction gave a greater time delay than the initial (before radiation) delay, and that the O and 180 degree directions gave equal delays but not as great as the 270 degree direction with the 90 degree radiation resulting in less time delay than that of the initial measurement; this indicates that the crystal should be radiated from an azimuth angle of 270 degrees. The amount of radiation from this angle is then determined as previously set forth. If approximately equal delays are encountered from two adjacent quadrants, 45 degree positions in the quadrants may then be utilized and the process of reradiating and remeasuring the crystal continued as set forth. If desirable the quadrants may 'be broken up into progressively smaller angles until essentially the exact azimuth angle for the arriving radiation is ascertained. Generally, it has been found to be unnecessary to use smaller than the 45 degree positions.

The illustrations of this invention previously set forth were with BC-cut quartz rod. Similar results have been obtained with X-cut quartz crystals. This method of improving the acoustic propagation in crystals may also be applied to other crystal delay lines such as those of A1 TiO MgO, MgAl O CdS, and ZnO.

What is claimed is:

1. The method of improving the acoustic response of single crystal cylindrical rod delay lines comprising:

(a) measuring the delay time of the crystal delay line;

(b) radiating the crystal rod from a radial direction with a determined amount of particle radiation such as neutrons or electrons;

(c) removing the radiation and remeasuring the delay time of the crystal;

(d) annealing the crystal to remove the effects of the radiation;

(e) changing the said radial direction of radiation, re-

' radiating with the said determined amount of radiation and remeasuring the delay time of the crystal for determining the preferred radial direction of radiation as indicated by a first maximum delay time;

(f) radiating the crystal with increasing amounts of radiation from the preferred radial direction and measuring the delay time until an approximately constant second maximum delay time occurs to provide improved acoustic response.

2. The method of improving the acoustic response of quartz single crystal cylindrical rod delay lines comprismg:

(a) measuring the delay time of the crystal delay line;

(b) radiating the crystal rod from a radial direction with a determined amount of X-ray radiation;

(0) removing the radiation and remeasuring the delay time of the crystal;

((1) annealing the crystal at approximately 500 degrees centigrade to remove the effects of the radiation; (e) changing the said radial direction of radiation, reradiating with the said determined amount of radiation, and remeasuring the delay time of the crystal delay line for determining the preferred radial direction of radiation as indicated by a first maximum delay time; and

(f) radiating the crystal from the said preferred radial direction with successive increasing step amounts of X-ray radiation, removing the radiation and measuring the delay time after each step, said successive step increases continuing until approximately a constant second maximum delay time is measured.

3. The method, as claimed in claim 4, wherein the length of the cylindrical crystal rod exposed to the X-ray radiation is not over 80 percent of the cylindrical length of the crystal.

References Cited Science News, Science Supplement, vol. 101, No. 2625, Apr. 20, 1945, p. 12.

ARCHIE R. BORCHELT, Primary Examiner c. E. CHURCH, Assistant Examiner US. Cl. X.R. 

